1. Field of the Invention
This invention relates generally to bandgap reference circuits and, more specifically, to a precision bandgap reference circuit which is insensitive to temperature, supply voltage and process variations.
2. Description of the Prior Art
FIG. 1 shows the most common CMOS bandgap reference circuit. The main problem with current CMOS bandgap reference circuits is that the output reference voltage varies due to temperature, supply voltage, and process variations. Furthermore, as can be seen from FIG. 1, the basic CMOS bandgap reference circuit has very low gain which may cause errors across the resistor/diode combination input and diode input. The basic CMOS bandgap reference circuit is also unbalanced. The drain to source voltages of the transistors are different since one is connected as a diode and one is not.
Therefore, a need existed to provide a precision bandgap reference circuit. The precision bandgap reference circuit must be insensitive to temperature, supply voltage and process variations. The precision bandgap reference circuit must be produced on a standard CMOS process. The precision bandgap reference circuit must also increase the gain in order to minimize errors across the resistor/diode combination input and the diode input. The output stage of the precision bandgap reference circuit must also be biased with a Proportional To Absolute Temperature (PTAT) current thereby generating a well controlled and insensitive bandgap reference circuit.